JP2008036492A - Coating method of bottle can with inner surface coating and coated bottle can by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a bottle can which eliminates the non-conformity such as difficulties to open bottle caps due to the high valve rotation torque before cutting the bridge and which reduces the rotation torque so as to easily open the bottle caps by reducing the frictional resistnce between the synthetic resin liner of caps and the inner surface coating of the curl top surface that is not conventionally recognized as a problem, and to provide a bottle can manufactured by the method. <P>SOLUTION: The inner coating method of the bottle can is characterized by applying the inner coating to which particulate wax is added on the opening including at least the curl top surface of the bottle can of the inner side of a bottomed cylindrical tube for aluminum bottle can having a thread for screwing the cap and the bottle can manufactured by the method is obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, the inner surface side of the bottomed cylindrical body of the bottle can having a screw for screwing the cap is coated with at least the curled top surface with an inner surface paint to which particulate wax is added. In addition, the present invention relates to a method for coating the inner surface of a bottle can that is easy to open by reducing the opening torque, and a bottle can manufactured by the method.

  In the conventional bottle can manufacturing process, the oil deposited on the aluminum can (bottomed cylinder) made by DI processing (squeezing and ironing) is degreased, and the zirconium-based chemical liquid is The base treatment of the zirconium-based chemical conversion film is performed by spraying on the inner and outer surfaces. After the chemical conversion treatment, the outer surface of the can body is printed and clear-coated in the printing process, and the inner surface of the can body is spray-coated in the inner surface coating process. Thereafter, necking, screwing and curling are performed.

By the way, aluminum bottle cans are made by punching a circular blank from an aluminum plate or aluminum alloy plate coated with lubricating oil wound in a coil shape, forming a cup with a press, etc., and then drawing and ironing (DI processing) Thus, the bottomed cylindrical body is processed with an extremely thin side wall. For this reason, when filling beverages mixed with gas such as beer, sparkling liquor, carbonated beverages etc., it is already positive pressure, but when filling beverages without gas mixed, Liquid nitrogen (nitrogen gas) is added before sealing to prevent the can from collapsing by making the internal pressure of the can higher than the atmospheric pressure.
However, if the internal pressure at the time of filling is too high, one or more bridges may be cut naturally after the can is sealed with a cap, so-called bridge breakage may occur. When a bridge break occurs, it cannot serve as evidence for opening the bridge.

  Many methods for increasing the strength of the bridge have been proposed as a method for solving such a problem of bridge breakage. However, all of them increase the necessary rotational force applied to the cap when the cap is opened, that is, the opening torque increases. There are problems that make it difficult. As a countermeasure, there has been proposed a bottle can that reduces the opening torque by setting the number of effective threads of the threaded portion to 2 in the circumferential direction where a majority of the bridges of the cap exist. In addition, in order to impart lubricity, a proposal has been made to coat the periphery of the opening of the bottomed cylindrical body for bottle cans with a composition in which a polymerized polyester / amino resin or a polyethylene wax is added [Patent Document] 1].

  Conventionally, the inner surface coating material for bottle cans is added with a small amount of wax for necking, screwing and curling. This wax is a plant carnauba wax or the like so as not to deteriorate the flavor of the contents. Plant-based carnauba wax is an excellent wax that does not affect the flavor properties of the contents.

  However, in the manufacturing process of the bottle can screw part, vegetable oil is applied to the can surface for screw processing lubrication, and then it is washed with a hot water shower. At that time, since the melting point of the carnauba wax in the inner surface coating film is around 80 ° C., the wax is partially melted and washed away, the slipping property of the inner surface coating film is deteriorated, and the cap canting torque of the bottle can is reduced. Troubles that are too high and difficult to open.

A synthetic resin liner is fitted on the inner surface of the cap of the bottle can to ensure the sealing performance of the bottle can. When opening the cap screwed into the bottle can, the synthetic resin liner and the top curl top of the bottle can are in pressure-bonded state. appear. This frictional resistance further increases when the wax on the inner surface coating film is partially melted and washed away to deteriorate the slipperiness.
This is presumably because a part of the wax or the like remaining at the time of sterilization treatment, retort treatment, or the like after filling the contents is fused with the cap liner. Since the torque when the cap is twisted to open the cap is the highest value, there is a demand for reducing this to be the opening torque.

JP 2002-302137 A

  The purpose of the present invention is to eliminate the problem that bottle cap cap opening torque is high and difficult to open, and in order to reduce the highest opening torque when twisting the cap to open the cap, it is completely ignored in the past. The bottle with reduced opening torque so that it can be opened easily even by the elderly and small people by reducing the frictional resistance between the synthetic resin liner of the cap and the inner surface coating film on the top of the curl. It aims at providing the manufacturing method of a can, and the bottle can manufactured by this method.

The present invention
[1] An opening including a portion that becomes a curled top surface of a bottle can on the inner surface side of a bottomed cylindrical body for an aluminum bottle can having a screw for screwing a cap is made of an inner surface paint to which particulate wax is added. The inner surface painting method of bottle cans, characterized by painting,
[2] The melting method of the particulate wax is 120 ° C. or higher, and the average particle size is 1 to 8 μm.
[3] The inner surface coating method for an aluminum bottle can according to the above [1] or [2], wherein the particulate wax is any one of polyethylene wax, polypropylene wax and Teflon (registered trademark) wax,
[4] The aluminum bottle can according to any one of the above [1] to [3], wherein the inner surface coating material is an inner surface coating material containing 0.1 to 2% by weight of particulate wax of the blended resin. Internal coating method,

[5] An opening including a curled top surface of the bottle can and a screw portion on the inner surface side of the bottomed cylindrical body for an aluminum bottle can having a screw for screwing the cap is added with particulate wax. A bottomed cylindrical body characterized by being coated with an internal paint,
[6] By developing an aluminum bottle can having a screw for screwing a cap, wherein at least the top of the curl is coated with a paint containing particulate wax. Solved the above problem.

  In the present invention, in order to lower the opening torque when the cap is twisted in an attempt to open the cap, by coating only the screw portion with the inner surface coating material to which particulate wax particles are added, it is completely ignored in the past. A method for producing a bottle can in which the frictional resistance between the synthetic resin liner of the cap that has not been made and the inner surface coating of the curl top surface is reduced, and the rotational torque is reduced so that it can be easily opened even by the elderly and dwarfs. We have succeeded in providing a bottle can manufactured by this method.

  Usually, the inner surface of a bottomed cylindrical body for aluminum or aluminum alloy bottle cans is painted by using one to three airless spray guns and spray nozzles to spray the water-based inner surface paint. Is adopted as a general spray coating method.

FIG. 1 shows a cross-sectional side view of the inner spray coating.
Conventionally, the same inner surface paint is sprayed from one or a plurality of airless spray guns. However, in the present invention, for example, in one gun (3rd gun in FIG. 1), a bottle can screw is formed with an inner surface paint added with polyethylene wax particles. Only the part corresponding to the rear screw part (mainly the top surface in contact with the liner of the synthetic resin cap) is painted, and the other inner surfaces are the other guns (1st gun, 2nd gun in FIG. 1). Paint with a well-known inner surface paint added with wax.
The portion corresponding to the curled portion (the top surface that comes into contact with the cap liner) and the screw portion after the bottle can screw formation is usually about 30 mm from the opening of the bottomed cylindrical body for the bottle can.

  The aqueous inner coating material used in the present invention is preferably an aqueous epoxy / acrylic / phenolic resin composition that can reduce the deterioration of the working environment due to evaporation of the organic solvent. As the wax to be added to the paint, there is a possibility that a small amount of the applied wax enters the contents of the bottle can, and therefore, waxes approved by the FDA are used. Further, the wax adhering to the outer surface of the bottle can is at least 120 ° C., preferably 140 ° C. or more, in order to reduce detachment in washing with hot water, non-stickiness, and detachment in sterilization after filling the contents A wax having a melting point of As such a wax, polyethylene wax, polypropylene wax, Teflon (registered trademark) wax and the like are preferable. The shape of the wax is powder, and the average particle size of the wax is usually 1 to 8 μm, particularly preferably about 1 to 6 μm. Commercially available wax may be used, and for example, AC polyethylene manufactured by Honeywell, USA can be used.

  The particulate wax has a spherical shape in the coating film when melted in the baking process of the paint, and also has a shape close to a spherical shape even when it does not melt, both of which protrude from the coating surface. It becomes fixed and the friction resistance between the cap liner and the can curl top surface is greatly reduced. In this case, since the coating thickness of the inner surface coating is about 7 μm, it seems that the wax is often detached from the coating when the average particle diameter of the wax is 6 μm or more. Moreover, when the average particle diameter of the wax is 1 μm or less, the number of spherical waxes that can be seen from the surface of the coating film decreases, and the effect of the slipperiness of the wax decreases.

The amount of the wax added is 0.1 to 2% by weight, preferably 1 to 1.8% by weight, in the coating resin. When the added amount of the wax is 2% by weight or more, it is difficult to uniformly disperse the wax in the paint, and there is a risk of adversely affecting the flavor of the contents. On the other hand, when the added amount of the wax is 0.1% by weight or less, the effect of improving the slipperiness due to the addition of the wax is lowered.
Although the decrease in the friction coefficient between the cap liner and the top surface of the bottle can has been ignored so far, it has been found that the frictional resistance between the cap liner and the top surface of the can curl has more influence than expected.

[Measuring method]
a. The melting point of the wax was measured with a differential scanning calorimetry apparatus manufactured by Pyris.
b. The average particle size of the wax was measured with a dynamic light scattering particle size analyzer manufactured by Malvern.
c. The friction coefficient of the inner surface coating film was measured with a Static Friction measuring instrument manufactured by HEIDON.
d. The opening torque of the cap was measured with an opening torque meter TNK-50B manufactured by SHIMPO.

[Examples 1 to 4]
As shown in Table 1, the melting point is 140 to 145 ° C. at a location from the can mouth corresponding to the threaded portion (including the curled top surface) of the bottomed cylindrical body for the aluminum bottle can with a capacity of 310 ml from the can mouth to about 30 mm. Then, an epoxy / acrylic / phenolic aqueous paint in which 1.5% by weight of polyethylene wax (AC polyethylene wax, manufactured by Honeywell, USA) having an average particle size of 1.0 to 7.0 μm was blended in the paint resin was applied. The portions other than the portion corresponding to the screw portion were painted and baked with a conventional epoxy / acrylic / phenolic water-based paint. The bottomed cylindrical body was molded into a bottle can, washed with a hot water shower and dried, and then the friction coefficient of the inner surface coating film and the cap opening torque were measured. The results are shown in Table 1.

[Comparative example]
The same treatment as in the examples except that instead of the high melting point wax in the examples, a conventionally used paint (carnauba wax: melting point 80 ° C., blending amount; 0.1 wt% blended in the coating resin) was used. Then, a bottle can was molded, and the friction coefficient of the inner coating film and the cap opening torque were measured in the same manner as in the Examples. The results are shown in Table 1.

  Compared with the comparative examples, in each of the examples, the polyethylene wax does not seem to be detached even after the hot water shower cleaning, and the lubricating effect of the wax prevents the blocking between the cap synthetic resin liner and the inner surface coating of the curl top surface. It was recognized that the cap opening torque was considerably low.

When twisting the cap to open the bottle can, the friction resistance between the cap's synthetic resin liner and the inner surface coating on the top of the curl, which was not considered a problem, was reduced to reduce the opening torque, which is the highest value. Attention has been paid to the development of a bottle can that is easy to open with no bridge breakage and low opening torque.
As a result, by reducing the frictional resistance, it has become possible to provide a wide range of bottle cans that can be easily opened by elderly people or weakly ill patients.

Cross-sectional side view during internal spray painting

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bottomed cylindrical body for bottle cans 2 1st inner surface spray gun 3 2nd inner surface spray gun 4 3rd inner surface spray gun

Claims (6)

  The opening including the part that becomes the curl top surface of the bottle can on the inner surface side of the bottomed cylindrical body for the aluminum bottle can having the screw for screwing the cap is coated with the inner surface paint to which particulate wax is added. A method for painting the inner surface of bottle cans.   The method for coating an inner surface of an aluminum bottle can according to claim 1, wherein the melting point of the particulate wax is 120 ° C or higher and the average particle diameter is 1 to 8 µm.   The method for coating an inner surface of an aluminum bottle can according to claim 1 or 2, wherein the particulate wax is any one of polyethylene wax, polypropylene wax and Teflon (registered trademark) wax.   The inner surface coating method for an aluminum bottle can according to any one of claims 1 to 3, wherein the inner surface coating material is an inner surface coating material containing 0.1 to 2% by weight of a particulate resin wax.   The inner surface of the bottomed cylindrical body for the aluminum bottle can having a screw for screwing the cap, the opening including the curled top surface of the bottle can and the screw portion is an inner surface paint to which particulate wax is added. A bottomed cylinder characterized by being painted. An aluminum bottle can having a screw for screwing a cap, wherein at least a curl top surface is coated with a paint containing particulate wax.

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